The present invention relates to extrusion dies of the cross-head type for applying uniform layers of coating materials to elongated, filament members, and more particularly to cross-head die apparatus for simultaneously applying visually distinguishable coating layers to a plurality of filament members. The invention also relates to methods thereof.
Electrical wires, optical fibers, and other elongated, filament members are commonly provided with coatings for insulating, shielding, and other purposes by an extrusion process utilizing apparatus known as a cross-head die. For purposes of discussion, it will be assumed that the members to be coated are electrical conductors, although it will be understood that the invention is not limited to employment with that type of filament members. The coating material is commonly an appropriate type of plastic and, in any case, is applied to the wire while in a molten or otherwise flowable condition.
Typical cross-head dies include a body portion having a through axial bore with which a radial bore communicates on one side. The wire is moved longitudinally through the axial bore, wherein its axis of travel is established by appropriate guide means, as the flowable coating material is injected through the radial and into the axial bore. Structure within the axial bore established a flow path causing the coating material to pass through an annular orifice, surrounding the wire in an essentially uniform coating as it exits the front end of the axial bore.
When electric wires, and other coated filament members, are placed in use it is often desirable to have some means of visually distinguishing between wires of different gage material or other physical or electrical properties, or simply to be able to identify individual wires of a group of wires at various points along their length. The coating materials may be color-coded to provide this attribute. Also, since the number of solid colors is limited, it is a common practice to provide multi-colored coating layers on a single wire. A layer including longitudinally extending, circumferentially distinct portions of different colors may be applied in a cross-head die by providing a plurality of radially extending bores communicating with the same axial bore at different positions about the periphery thereof. Of course, the coating materials injected through all of the radial bores are applied to only the single wire which is moved through the axial bore with which the radial bores communicate.
In some cross-head dies, two or more axial bores may be provided in the die body to permit simultaneous coating of a plurality of wires. At least one radial bore communicates solely with an associated axial bore; more than one radial bore communicates with each axial bore wherein more than one coating material is to be applied to the wire moved therethrough. Thus, while it is possible to coat a plurality of wires simultaneously in a single die body, and to apply multi-color coatings to one or more wires, the number of connections of the vessels containing the coating materials to the die body, and therefore the cost of fabricating the die body, and associated apparatus, increases accordingly.
It is a principal object of the present invention to provide novel and improved apparatus and methods for applying multi-colored coating layers simultaneously to a plurality of wires in a single cross-head die body as set forth in our claims.
Other objects will in part be obvious and will in part appear hereinafter.